What Class 8 is for
There is a fashion for starting JEE coaching in Class 8 with JEE-style questions. I do not do that, and I will tell you why. A Class 8 student who is drilled on questions they do not have the tools for learns to guess patterns instead of to think. It looks impressive for a term and it costs two years later.
Class 8 is the year one specific thing happens: mathematics stops being arithmetic and becomes algebra. A student who makes that shift cleanly can be taught almost anything afterwards. A student who does not spends Class 9, 10, 11 and 12 doing physics with a handbrake on, because every formula rearrangement is a small crisis.
So the Class 8 foundation year is mostly about making three things automatic — algebra, units, and chemical notation — inside whatever board syllabus your child's school is already doing.